Diptera: Chironomidae) in the Sediment of Plešné Lake (The Bohemian Forest, Czech Republic): Palaeoenvironmental Implications
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Biologia, Bratislava, 61/Suppl. 20: S401—S411, 2006 Section Zoology DOI: 10.2478/s11756-007-0076-6 Holocene subfossil chironomid stratigraphy (Diptera: Chironomidae) in the sediment of Plešné Lake (the Bohemian Forest, Czech Republic): Palaeoenvironmental implications Jolana Tátosová 1,JosefVeselý2 & Evžen Stuchlík3 1Institute for Environmental Studies, Faculty of Science, Charles University in Prague, Benátská 2,CZ-12801 Prague, Czech Republic; e-mail: [email protected] 2Czech Geological Survey, Geologická 6,CZ-15200 Prague 5, Czech Republic 3Hydrobiological Station, Institute for Environmental Studies, Charles University in Prague, P.O. Box 47,CZ-38801 Blatná, Czech Republic Abstract: A faunal record of chironomid remains was analyzed in the upper 280 cm of a 543 cm long sediment core from Plešné jezero (Plešné Lake), the Bohemian Forest (Šumava, B¨ohmerwald), Czech Republic. The chronology of the sediment was established by means of 5 AMS-dated plant macroremains. The resolution of individual 3-cm sediment layers is ∼115 years and the analyzed upper 280 cm of the sediment core represent 10.4 cal. ka BP. As the results of DCA show, two marked changes were recorded in the otherwise relatively stable Holocene chironomid composition: (1) at the beginning of the Holocene (ca. 10.4–10.1 cal. ka BP) only oligotrophic and cold-adapted taxa (Diamesa sp.,M.insignilobus-type, H. grimshawi-type) were present in the chironomid assemblages, clearly reflecting a cool climate oscillation during the Preboreal period, and (2) during an event dated in the interval 1540–1771 AD, when most taxa vanished entirely and only Zavrelimyia sp. and Procladius sp. were alternately present accompanied by Tanytarsus sp. Although, the age of this event is in agreement with the dating of the Little Ice Age, the most probable reason for the elimination of many chironomid taxa was very low sums recorded in this part of the sediment, rather than cool conditions connected with the LIA. Variations in the chironomid fauna after the Preboreal period were reflected mainly by changes in abundances of dominant taxa rather than by changes in species composition. These variations could be explained by: (1) climatic changes, namely temperature and amount of rainfall resulting in oscillations in lake level, with changes in the occurrence of macrophytes in the littoral and (2) increasingly dense afforestation which led to a considerable input of organic material into the lake and a subsequent increase in the trophic status of the lake water. Key words: Chironomidae, glacial lake, climate changes, palaeoenvironmental reconstruction, palaeolimnology. Introduction et al., 1997; Brooks & Birks, 2000). Chironomid lar- vae possess chitinized head capsules that are resistant Larvae of Chironomidae (Insecta: Diptera) colonize all to decomposition. Consequently, fossilized chironomid freshwater systems, from large lakes to the smallest head capsules tend to be well preserved in lake sed- ponds, and often dominate the benthos. This family iment over thousands of years, and can generally be is noted for its taxonomic richness, with nearly 10,000 identified to genus or, more rarely, to species-group species distributed globally (Cranston, 1995), repre- level. This offers the possibility of using the fossil chi- senting more than 20% of all freshwater insects in rivers ronomid record to infer past environmental conditions and lakes. As a result of their short generation times in lakes. Knowledge of modern chironomid ecology al- and the dispersal capacity of the winged adults, chi- lows the use of chironomid subfossils for the recon- ronomids respond rapidly to changes in a wide variety struction of palaeoproductivity (Brodersen & Linde- of environmental variables (Walker, 2001). Transfer gaard, 1999), acidification (Brodin & Gransberg, functions have been developed for a range of environ- 1993; Schnell & Willassen, 1996), palaeosalinity mental parameters including salinity (Heinrichs et al., (Walker et al., 1995) and, more recently, summer tem- 2001), dissolved oxygen (Quinlan & Smol, 2002) and perature variations (Brooks & Birks, 2001; Kor- nutrients (Brodersen & Lindegaard, 1999; Brooks hola et al., 2002; Heiri et al., 2003; Larocque & et al., 2001); however, over large climatic gradients, air Hall, 2004; Heiri & Lotter, 2005). temperature is often the best explanatory variable for The preliminary results presented here form part chironomid distribution (Lotter et al., 1997; Walker of a multi-disciplinary project investigating the biotic c 2006 Institute of Zoology, Slovak Academy of Sciences S402 J. Tátosová et al. Table 1. Radiocarbon dating of plant remains. Laboratory code Depth (cm) CAR yr. BP Range 1) cal. ka BP Intercept with cal. ka BP 2) NZA–9645 51–54 2005 ± 60 2.11–1.82 1.95 NZA–9317 105–108 3637 ± 60 4.13–3.82 3.95 NZA–13686 114–117 3949 ± 50 4.52–4.24 4.42 NZA–11663 141–144 4733 ± 55 5.59–5.32 5.53 NZA–9599 234–237 8264 ± 65 9.43–8.99 9.28 Explanations: CRA – Conventional Radiocarbon Age; NZA – Laboratory Code of the Rafter Radiocarbon Lab., New Zealand; 1) 95% confidence thresholds of ka BP; 2) REIMER et al. (2004). and abiotic responses to climate changes that occurred but did not survive the period of maximum acidification and during the Late Glacial and Holocene in the Bohemian at present the lake is fishless. Forest (Šumava, B¨ohmerwald), Czech Republic. Similar studies are available for many areas of Europe (Gan- Methods douin & Franquet, 2002; Korhola et al., 2002; Porinchu & Cwynar, 2002; Lotter & Birks, 2003; In 1991, a 543 cm long core was collected by R. Schmidt (In- Brooks & Birks, 2004; Larocque & Hall, 2004; stitute for Limnology of the Austrian Academy of Sciences, Langdon et al., 2004; Dalton et al., 2005; Velle Mondsee, Austria) with a modified Kullenberg piston corer et al., 2005), but have never been done on lakes of close to the deepest part of the lake. The core was sub- glacial origins in the Czech Republic. Similar studies sampled every 3 cm and samples were continuously stored at 4 ◦C. A faunal record of chironomid remains was analyzed were published by Veselý et al. (1993), Veselý (1998, in the upper 280 cm. For analyses, a known weight of wet Pražáková & Fott Bitušík & ◦ 2000), (1994) and sediment was deflocculated in 10% KOH at 60 C for 20 min Kubovčík (2000). However, all of these concentrate and then washed with distilled water onto sieves with 230 on changes during shorter periods than are presented in µmand86µm mesh-size in order to facilitate the sorting this paper. The first integrated information on the mod- and picking of head capsules. The material was transferred ern chironomid fauna in these lakes of the Bohemian from the sieves into a plankton counting tray and all head Forest was given by Bitušík & Svitok (2006). capsules were picked with either fine forceps or a needle × The main aim of this paper is to describe the using a stereomicroscope at 25 magnification. After dehy- dration in isopropyl alcohol, head capsules were mounted on Holocene chironomid stratigraphy of Plešné jezero slides in Euparal mounting medium. (Plešné Lake) and to provide a preliminary Holocene Taxonomy mainly follows WIEDERHOLM (1983), reconstruction of key environmental conditions in this SCHMID (1993), BITUŠÍK (2000) and RIERADEVALL & area. BROOKS (2001). Members of the tribe Tanytarsini were re- viewed using the description given by HEIRI et al. (2004). Study site Concentrations of organic carbon (C) in lyophilized sub-samples were analyzed with a TOC 5000A analyzer. Plešné Lake is a small lake of glacial origin (7.6 ha, max. depth 17 m) located at an altitude of 1087 m a.s.l. and Chronology situated in a relatively remote and uninhabited part of A total of seven terrestrial plant remains were isolated from the Bohemian Forest (48◦47 N, 13◦52 E) in C Europe. five levels of the Holocene sediment and dated by the AMS- Thebedrockofthecatchment(0.67km2) is formed by radiocarbon method in the Rafter Radiocarbon Laboratory, Lower Hutt, New Zealand in the year 2000. Errors of dating granite, and is covered with a thin layer of lithosol, pod- 14 zol and spododystric cambisol (JANSKÝ et al., 2005). The by C-methods are ≤ 200 years and the age of the core catchment is steep and forested, with Picea excelsa domi- bottom was ∼14.5 ka BP. The resolution of individual 3-cm nating. The average annual and July air temperatures are sediment layers is ∼115 years in the Holocene (Tab. 1; for 4.4 and 13.1 ◦C, respectively (Czech Hydrometeorological more details see PRAŽÁKOVÁ et al., 2006). Institute), and the period of ice-cover averages 135 days −1 −1 yr . The present average TP loading (11 µgL ) suggests Data analysis mesotrophic conditions in the lake. The chironomid percentage diagrams were created using Plešné Lake was partially affected by atmospheric acid- TILIA version 2.0.2 (GRIMM, 2004) and the zones were de- ification in the early 1960s, and during the peak of acidifi- fined using the CONISS (constrained incremental sum of cation in 1980s the pH of lake water dropped below 4.7 squares cluster-analysis) program available in TILIA. In ad- (VESELÝ &MAJER, 1996; KOPÁČEK et al., 1998). At the dition, Detrended Correspondence Analysis (DCA) was ap- present time, the lake is in the process of chemical and bi- plied to the chironomid data. DCA was performed using the ological recovery (MAJER et al., 2003; VRBA et al., 2003; program CANOCO version 4.5A (Ter BRAAK &SMILAUER, th NEDBALOVÁ et al., 2006). At the end of 19 century, Salmo 2003) and square-root transformation of species data and trutta L., 1758 was introduced to the lake (VESELÝ, 1994), down-weighting of rare taxa were used. Subfossil chironomids from Plešné Lake S403 Results mulative variance in the chironomid data. The sample scores of these axes were plotted on a time scale, with Taxonomy scaling in the original standard deviation units.